Display screen or portion thereof with a graphical user interface



The FIGURE is a front view for a display screen with a graphic user interface showing my new design.

The broken lines around the FIGURE showing a display screen or portion thereof are included for the purpose of illustrating environmental structure. The broken line showings of the text, numbers, symbols, function marks, and images in FIGURE are included for the purpose of illustrating portions of the display screen with a graphic user interface. The broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 